The present invention is described in the following on the basis of a plurality of sensors from the automotive sector. However, it is not restricted to these sensors, but may also be realized in connection with sensors from other fields of application.
The triggering of a restraining apparatus in a motor vehicle usually occurs as a function of various parameters such as the severity of the impact and the position and the weight of the passengers. It is useful to take the respective belt force into consideration as well, which is explained in greater detail in the following on the basis of an example.
For the triggering of a multi-stage airbag and for the triggering of belt tighteners, data may be acquired regarding the profile of the individual passengers, which allows conclusions as to their weight. For this purpose, a force sensor, or a force-sensor array, may be used, which is installed in the seat and realized, for example, in the form of a sensor mat having pressure-sensitive sensor cells. The sensor cells are arranged in a matrix and may be triggered individually, so that it is possible to detect the pressure distribution in the seat in the form of a value matrix. The heavier a person, the more heavily the seat material is compressed and the higher the number of activated sensor cells. Of course, the pressure value detected by a sensor cell is also dependent on the respective pressurization. In evaluating the pressure data detected by the individual sensor cells of the sensor mat, the number of the activated sensor cells is therefore taken into consideration as well, in addition to the individual pressure values. A control device, which is also installed in the seat, carries out the evaluation. The result of the evaluation is transmitted to the air bag control device, so that the individual seat occupancy may be taken into consideration in the triggering of the restraining means. This method is largely independent of external conditions such as cold or wear. Nevertheless, the force-sensor array should be calibrated at regular time intervals in order to ensure constant measuring results at a given weight force.
A child seat may be detected on the basis of its seat profile, which does not resemble that of a person. However, if a child seat is strapped in with a strong belt force of approximately 150 N, it is pressed into the seat with such force that its seat profile is distorted and it appears heavier than it actually is.
However, a belt force of more than 30 N may not really be applied over a long period of time when a person is strapped in since the belt usually yields. Such a high belt force may also be so uncomfortable that no passenger would maintain it. Therefore, when the belt force exceeds a certain threshold value it may be assumed with a high degree of certainty that it is not a person that is strapped in but a child seat or some other object. On the basis of the data of the applied belt force, it thus may be possible to implement an occupancy detection to a certain extent.
A prerequisite for being able to consider the force exerted by the belt when evaluating the pressure data is the use of a belt-force sensor. However, for this purpose it may be necessary to ensure that a measuring value of the belt-force sensor is constant in the long term or over the service life of the motor vehicle at a given belt force. This may be problematic in practice, in particular, in static belt-force sensors, since it is often the case here that time drift occurs in the measured values.